The present invention relates to a color picture image reading device. More particularly, the present invention relates to a color picture image reading device for applying color correction processing to color image data obtained by a color image sensor which includes a plurality of color image sensor chips disposed on a chip with color filters and connected in series.
A color picture image reading device is, in general, composed of a picture image reader for reading out a picture image in analog form and outputting analog R,G,B signals, having a light source and an image sensor, a digital processor for converting the R,G,B signals into R,G,B digital data, and a correction means for applying required correction to the R,G,B digital data.
An image sensor for optically reading out an original picture image information is required to have a certain degree of length relative to a main scanning direction of reading out. For example, in order to read out an original picture image written on a paper of A 4 size in a closely adhered type image sensor, at least a length of 210 mm for the shorter width of the A 4 size is necessary. However, it is difficult to prepare an image sensor having such a length in one chip, and therefore the cost is high. Therefore, there is used such a method as shown in FIG. 2, in which a plural number of chips of image sensors which are each shorter than the total required length are connected in series, and used as a single image sensor.
Conventionally when an image sensor constituted of a plural number of sensor chips as described above is used, there is generally a discrepancy in color characteristics between the sensor chips. Particularly, when a sensor chip on-chipped with a color filter is used, a discrepancy in the spectroscopic transparency characteristics of the color filters, results. Thus if a uniform manuscript, without pattern or the like, has been read out, discrepancy is generated in color picture image signals between the chips, even when shading compensation is applied thereto. Consequentially, when the color picture image is reproduced using the color picture image signals as they are, discrepancy is generated in the color picture element data in correspondence to the color characteristics of the chips read out, with the result that, a smooth reproduced picture image can not be obtained. Therefore, in order to correct the discrepancy in color characteristics of a plural number of sensors chips, color correction corresponding to each respective chips is necessary. The color picture element data are in general composed of three data, that is R,G,B data and the correction coefficients used in the color correction to the color picture element data forms a 3.times.3 correction matrix. The color correction is carried out by the multiplication between the R,G,B data and the correction matrix.
On the other hand, the conventional color image reading device assumes in general that the color image can be reproduced by various output devices (CRT, color printer, etc.) by being connected to these devices.
In such a situation, for the output device (such as a CRT, color printer, etc.), since the color characteristics are different for each particular output device, color correction specific to the respective output device is also necessary. This type of color correction is carried out in the same way that the color correction of the discrepancy in the color characteristics between the sensor chips is carried out.
As described above, when the discrepancy of the color characteristics between the sensor chips and the difference of the color characteristics of a respective output device are intended to be corrected, the combinations thereof become very abundant. For example, when it is assumed that the number of sensor chips constituting one line sensor is m pieces, and the kinds of the output devices are n kinds, then, when the correction is to be carried out with color correction coefficients corresponding to all of these, the number of combinations necessary for the color correction becomes m.times.n. The resulting number of correction coefficients becomes m.times.n.times.9 owing to the fact that each correction requires 9 coefficients. Conventionally when all of these color correction coefficients are to be memorized, a vast number of memories are required, and the expense for determining the color correction coefficient therefore increases.